Necessary Information

• Required compressive strength at 28days: 30 Mpa• Type of structure: mass concrete, beam, column.• Maximum size of aggregate: 20 mm• Fineness modulus of sand: 2.7• Dry-rodded weight of coarse aggregate: 1600 kg/m3

• Moisture absorption: 2% for coarse aggregate and 1.5% for fine aggregate

Fineness Modulus (FM)

( % )100

accumulative retained on stadard sievesFM

where the standard sieve sizes are No.100 (0.15 mm), No.50 (0.3 mm), No.30 (0.6 mm), No.16 (1.18 mm), No.8 (2.36 mm), and No.4 (4.75 mm)

Step 1

Estimate w/c based on required 28 days compressive strength

0.54

30 MPa = 4350 psiw/c = 0.54

1.

Step 2

Obtain slump value based on types of construction

75 – 100 mm 2.

Step 3

Estimate amount of water requirement for mixing based on maximum size of

aggregate and slump value

20 mm

195 kg/m3

Step 4

Calculation of cement content based on required water and w/c values

360 kg/m3

4.

Step 4

Estimate weight of aggregates based on unit weight of fresh concrete

Unit weight of fresh concreteMaximum aggregate size (mm)

Unit weight (kg/m3)

10 2285

20 2355

40 2420

Unit weight = Cement + Water + Aggregates

1800 kg/m3

Step 5

Calculate coarse aggregate content based on volume of dry-rodded and dry-

rodded weight of coarse of aggregate

Coarse aggregate content

(CA) = (V) x (CA dry-rodded wight)

(CA) = coarse aggregate

(V) = Volume of dry-rodded coarse aggregate per cubic meter of concrete

(CA dry-rodded unit weight) = 1600 kg/m3

1008 kg/m3

Step 6

Calculate fine aggregate content

Fine aggregate content

FA = Total aggregates – CA 792 kg/m3

Step 7

Calculate net weight of fine aggregate based on its moisture absorption

Net weight of fine aggregate

Net FA = FA x (1+MAf)

Net FA = 792 x (1+ 0.015) = 804 kg/m3

MAf: moisture absorption or moisture content of FA

Step 8

Calculate net weight of coarse aggregate based on its moisture

absorption

Net weight of coarse aggregate

Net CA = CA x (1+MAc)

Net CA = 1008 x (1+ 0.02) = 1028 kg/m3

MAc: moisture absorption or moisture content of CA

Step 9

Calculate net weight of water based on FA and CA and their moisture

absorptions

Net weight of water

Net W = W – FAx(MAf) – CAx(MAc)

Net W = 195 – 792(0.015) – 1008(0.02) = 163 kg/m3

Step 10

Adjust the concrete ingredient contents

Cement = 360 kg/m3

Fine aggregate = 804 (800 kg/m3)

Coarse aggregate = 1028 (1030 kg/m3)

Water = 163 (160 kg/m3)

Slump = 75 – 100 mm

Strength (28days) = 30 MPa